The invention relates generally to barrier layers, composite articles comprising the barrier layers, and methods of making the same. The invention also relates to devices sensitive to chemical species and especially electroactive devices comprising the composite articles.
Electroactive devices such as electroluminescent (EL) devices are well-known in graphic display and imaging art. EL devices have been produced in different shapes for many applications and may be classified as either organic or inorganic. Organic electroluminescent devices, which have been developed more recently, offer the benefits of lower activation voltage and higher brightness, in addition to simple manufacture and thus the promise of more widespread applications compared to inorganic electroluminescent devices.
An organic electroluminescent device is typically a thin film structure formed on a substrate such as glass, transparent plastic, or metal foil. A light-emitting layer of an organic EL material and optional adjacent semiconductor layers are sandwiched between a cathode and an anode. Conventional organic electroluminescent devices are built on glass substrates because of a combination of transparency and low permeability to oxygen and water vapor. However, glass substrates are not suitable for certain applications in which flexibility is desired. Flexible plastic substrates have been used to build organic electroluminescent devices. However, the plastic substrates are not impervious to environmental factors such as oxygen, water vapor, hydrogen sulfide, SOx, NOx, solvents, and the like, resistance to which factors is often termed collectively as environmental resistance. Environmental factors, typically oxygen and water vapor permeation, may cause degradation over time and thus may decrease the lifetime of the organic electroluminescent devices in flexible applications. Previously, the issue of oxygen and water vapor permeation has been addressed by applying alternating layers of polymeric and ceramic materials over the substrate. The fabrication of such alternating layers of polymeric and ceramic materials requires multiple steps and hence is time consuming and uneconomical.
Therefore, there is a need to improve the environmental resistance of substrates in electroactive devices such as organic electroluminescent devices and to develop a method of doing the same, in a manner requiring a minimal number of processing steps.